1. Field of the Invention
The present invention relates to a control system for a hydraulic work machine, and more particularly the present invention relates to the monitoring of potential and kinetic energies in movable elements of a hydraulic work machine, and to the control of hydraulic energy added to the hydraulic system.
2. Description of the Related Art
Hydraulics has a history practically as old as civilization itself. Hydraulics, more generally, fluid power, has evolved continuously and been refined countless times into the present day state in which it provides a power and finesse required by the most demanding industrial and mobile applications. Implementations of hydraulic systems are driven by the need for high power density, dynamic performance and maximum flexibility in system architecture. The touch of an operator can control hundreds of horsepower that can be delivered to any location where a pipe can be routed. The positioning tolerances can be held within thousandths of an inch and output force can be continuously varied in real time with a hydraulic system. Hydraulics today is a controlled, flexible muscle that provides power smoothly and precisely to accomplish useful work in millions of unique applications throughout the world.
Work machines are commonly used to move heavy loads, such as earth, construction material, and/or debris. These work machines, which may be, for example, excavators, wheel loaders, bulldozers, backhoes, telehandlers and track loaders, typically include different types of work implements that are designed to perform various moving tasks. Work implements may be, for example, a loader, shovel, bucket, blade, or fork. For the purposes of the present disclosure, the term “work implement” may also include the individual components of the work implement, such as a boom or stick. The work implements of these work machines are commonly moved by hydraulic actuators powered by hydraulic systems, which use pressurized fluid to move the work implements.
In many situations, the work implement of the work machine is raised to an elevated position. As the work implement may be relatively heavy, the work implement gains significant potential energy when raised to the elevated position. When the work implement is released from the elevated position the potential energy is usually converted to heat when the pressurized fluid is throttled across a valve and returned to the tank. Some of the potential energy of a work implement in an elevated position may be captured by redistributing that energy into an accumulator as a volume of pressurized hydraulic fluid. The stored energy can be used to perform useful work at a later time.
In addition to potential energies associated with elevated implements of work machines, there may be substantial kinetic energy in implements moving linearly or rotatively at points in a work cycle. Examples of such points in work cycles include: a rapid decent of a work implement from an elevated position to a lower position, and the rotation of a work machine superstructure commonly referred to as the swing function. Upon deceleration of the moving work implement, some of the kinetic energy of a work implement in motion may be captured by redistributing that energy into an accumulator as a volume of pressurized hydraulic fluid. The stored energy can be used to perform useful work at a later time.
Hydraulic transformers known in the art are designed to be used in conjunction with constant or semi-constant supply pressure as the energy source. The energy source may be driven by any of a variety of prime movers such as a diesel engine, gasoline engine, or an electric motor, and the energy supplied by the energy source may be supplemented by energy delivered by a hydraulic accumulator. Typically, however, there are no means by which a prime mover is governed to add energy only up to a pressure level less than a preset supply pressure.
In order to take full advantage of the benefits allowed by the digital hydraulic system, it is necessary to control the energy input into the hydraulic system.
In the event that a work implement has substantial potential and/or kinetic energy, it is advantageous in terms of energy efficiency to maintain a capacity for energy storage in the hydraulic accumulator approximately equal to the cumulative potential and kinetic energies of the work machine such that a maximum amount of potential and kinetic energy may be redistributed to the accumulator.
What is needed in the art is a control system that controls hydraulic energy input by the prime mover based on potential and kinetic energies of the work machine.